To solve the problem of state evaluations of small- and medium-span bridges such as concrete continuous girder bridges, this paper developed an extended model based on game theory. Aiming at Nash equilibrium, the combined weighting–fuzzy hierarchical comprehensive evaluation model was constructed by the combination of the analytic hierarchy process and the entropy weight method, which was corrected using the BP neural network. A three-span prestressed concrete continuous girder bridge in Wuhan was evaluated using health monitoring data and manual inspection information and compared to the results obtained using the traditional methods. The evaluation results showed that the error between the first-order frequency and the measured frequency was reduced from 17.95% to 9.00% and the bridge’s overall state score was 89.72. The evaluation model constructed by the method in this paper can take into account the contents of health monitoring and manual detection and coordinate the subjective and objective weights. Compared to the results of the analytic hierarchy process model and the fuzzy comprehensive evaluation model, the proposed model is reliable and applicable.

In composite structures or complex concrete members, some concrete bears multiple forces, called core concrete. The properties of the core concrete are variable under complex stress conditions, which will influence the structure performance analysis. Therefore, it is necessary to establish an accurate and theoretical constitutive model of concrete under complex stress conditions. The elastic–plastic properties of concrete in complex stress conditions were analyzed first. Then, the failure criterion of concrete in complex stress conditions was discussed to identify the key parameters. And the relationship between the stress–strain curve and failure criterion was analyzed through mathematical derivation. Finally, the multi-dimensional iterative constitutive model of concrete under complex stress conditions was established and verified. Based on the analysis results, the concrete under multi-axial stress conditions shows a spindle-shape stress envelope diagram. The failure criterion should be established by the analysis of concrete under high multi-axial compression conditions, tension–compression conditions, and shear–compression conditions. The plastic modulus is the key to reflecting the plastic strain development trend and the stress–strain relationship.